- 1868) RAMALINA RETICULATA 411 
minal portions from dry herbarium material, and measured the 
expansion which took place when water was brought into contact 
withthem. He found that the expansion was from 20 to 43 per 
cent, and the more rapid the thinner the pieces. All parts, old 
aswell as young, expand on wetting ; all parts expand unequally 
ifthe water is unequally distributed over them ; and if water is 
applied to only one side or edge of the thallus, or thallus frag- 
ment, that side will expand first and most, the transfer of water 
from part to part being comparatively slow. Such unequal 
expansions also occur in nature, because raindrops fall first on 
eS parts, then on others, though during a rain-storm of longer 
duration all parts become uniformly moistened. The unequal 
Wetting and consequent unequal expansions develop strains which 
lend to pull apart the thallus, the moist, soft parts pulling 
gah and away from the dry, stiff parts in all directions. The 
aed of the hyphe run longitudinally, the outer ones more 
gularly than those within; and the thallus is thin. 
a of wetting is that the thallus increases somewhat 
.. ness, more in length, and most (proportionally ) in 
- For example, a thallus branch, which I measured, was 
oe | 35 Te 
Oe ode 
1} inches long ; 
Inch broad when air dry, - - 
137 inches long 42.8™™ 
i inch broad when soaked for 3 minutes In cold water, - 10.3" 
#, inch=increase in length=7.1""=20 Pe cent. 
34 inch=increase in breath=3.2""=44 per cent.’ 
meet evident reason for this greater proportional eat 
Water. ; € breadth is that the gelatinous material, on absorbing 
verse} . ee by less resistance to swelling outward 
hadi against the air, than longitudinally against other 3 a 
the matter and the hyphe towards the tip and the base trom 
Wetted part. 
have ae the unequal expansions, 
€ roughly measured and indicat 
of which I 
the proportions 
4 table, Lutz 
ed in the above 
7 see : 
The metric figures in this table are calculated from the figures 10 inches, which 
Were obt 
ai , 
ned by measurement. 
